13C NMR study of the ‘‘bilayer’’ phase transitions in (C10H21NH3)2CuCl4

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Abstract
The two structural phase transitions in the perovskite type layer structure compound (C10H21NH3)2CuCl4 have been studied by single crystal 13C NMR. The paramagnetic shifts due to the Cu++ ions have been evaluated and subtracted from the experimental data to yield the 13C chemical shift tensors as a function of temperature. The results show in agreement with the DTA data that the transition from the low temperature to the intermediate temperature phase is connected with a partial melting of the alkylammonium chains and the vanishing of the average chain tilt, whereas the transition to the high temperature phase is accompanied by the onset of flipping of the polar heads and an associated rotation of the chains around the long axis. The two transitions are thus analogous to the ones found in lipid bilayer membranes and (C10H21NH3)2CdCl4 but the sequence of the two successive transitions is exchanged.